At present, the portable electronic apparatuses with liquid crystal display devices, such as mobile phones, hand-held computers, and laptops, are increasingly used. At some times, a user needs to share images displayed on a portable electronic apparatus with other people; while at other times, the user does not hope that others can see the images for the purpose of personal privacy protection. Therefore, in order to satisfy the two demands at the same time, a display device with a wide-narrow viewing angle switching function is needed.
FIG. 1 schematically shows a traditional liquid crystal display device with a wide-narrow viewing angle switching function when an upper substrate electrode is not applied with a bias voltage. As shown in FIG. 1, the liquid crystal display device in the prior art comprises an upper substrate 10, a blue phase liquid crystal layer 30, and a lower substrate 20. The upper substrate 10 and the lower substrate 20 are arranged parallel to each other, and each pixel structure is divided into a main pixel used for displaying and a sub pixel used for switching the viewing angle. The upper substrate 10 comprises an upper substrate glass layer 11, an upper substrate quarter-wave plate 12, an upper substrate half-wave plate 13, and an upper substrate polarizer 14. Similarly, the lower substrate 20 comprises a lower substrate glass layer 21, a lower substrate quarter-wave plate 22, a lower substrate half-wave plate 23, and a lower substrate polarizer 24. Pixel electrodes 25 and common electrodes 26 are arranged alternately on the lower substrate glass layer 21 in the regions where the main pixel and the sub pixel are located, and an upper substrate electrode 15 is arranged on a lower surface of the upper substrate glass layer 11 only in the region where the sub pixel is located. In the liquid crystal display device, the wide-narrow viewing angle switching function can be realized through applying the bias voltage to the upper substrate electrode 15 or not.
Specifically, still as shown in FIG. 1, when the bias voltage is not applied to the upper substrate electrode 15, the upper substrate electrode 15, the pixel electrodes 25 and the common electrodes 26 all have a zero electric potential. At this time, blue phase liquid crystal molecules in the main pixel area and blue phase liquid crystal molecules in the sub pixel area are all optically isotropic. The backlight that enters from the lower substrate 20 cannot pass through the upper substrate polarizer 14 and the lower substrate polarizer 24. Therefore, when the bias voltage is not applied, there is no light leakage when the liquid crystal display device is in a dark state, and the liquid crystal display device has a good dark state, so that a wide viewing angle can be realized.
As shown in FIG. 2, when the bias voltage is applied to the upper substrate electrode 15, the pixel electrodes 25 and the common electrodes 26 still have a zero electric potential. At this time, the blue phase liquid crystal molecules in the main pixel area are still optically isotropic. However, a vertical electric field can be generated between the upper substrate electrode 15 and the pixel electrodes 25 as well as between the upper substrate electrode 15 and the common electrodes 26 respectively. The blue phase liquid crystal molecules in the vertical electric field would deflect, and thus the blue phase liquid crystal molecules are in a vertical alignment state. When the backlight which enters from the lower substrate 20 normally passes through the blue phase liquid crystal layer 30, a polarization state of the blue phase liquid crystal molecules does not change, and thus the backlight cannot pass through the liquid crystal cell. When the backlight which enters from the lower substrate obliquely passes through the blue phase liquid crystal layer 30, the polarization state of the blue phase liquid crystal molecules would change, and thus some backlight would pass through the liquid crystal cell. Therefore, when the bias voltage is applied to the upper substrate electrode, there is the light leakage when the liquid crystal display device is in a dark state, so that a narrow viewing angle can be realized.
The defect of the aforesaid liquid crystal display device is that there is a viewing angle switching dead area in the display device. The viewing angle switching dead area is the non-switchable area as shown in FIG. 3. As shown in FIG. 3, when the bias voltage is applied to the upper substrate electrode 15, the oblique light in the non-switchable area can only pass through the optically isotropic blue phase liquid crystal molecules in the main pixel area, but cannot pass through the blue phase liquid crystal molecules in the vertical alignment state in the sub pixel area. Since the wide-narrow viewing angle switching function can only be realized with respect to the oblique light which passes through the blue phase liquid crystal molecules in the vertical alignment state in the sub pixel area, the non-switchable area is the aforesaid viewing angle switching dead area. The viewing angle control effect of the liquid crystal display panel is poor due to the existence of the viewing angle switching dead area.